Binders for wet and dry lamination of battery cells

ABSTRACT

Cell stacks are presented that include binders for wet and dry lamination processes. The cell stacks, when laminated, produce battery cells (or portions thereof). The cell stacks include a cathode having a cathode active material disposed on a cathode current collector. The cell stacks also include an anode having an anode active material disposed on an anode current collector. The anode is oriented towards the cathode such that the anode active material faces the cathode active material. A separator is disposed between the cathode active material and the anode active material and comprising a binder comprising a PVdF-HFP copolymer. In certain instances, an electrolyte fluid is in contact with the separator. Methods of laminating the cell stacks are also presented.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of U.S. patent applicationSer. No. 15/727,988, entitled “Binders for Wet and Dry Lamination ofBattery Cells,” filed on Oct. 9, 2017, which is a continuation of U.S.patent application Ser. No. 15/449,494, entitled “Binders for Wet andDry Lamination of Battery Cells,” filed on Mar. 3, 2017, now U.S. Pat.No. 9,786,887, which is a continuation-in-part of U.S. patentapplication Ser. No. 15/375,905, entitled “Binders for Wet and DryLamination of Battery Cells,” filed on Dec. 12, 2016, which claims thebenefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent ApplicationSer. No. 62/303,276, entitled “Binders for Wet and Dry Lamination ofBattery Cells,” filed on Mar. 3, 2016. The content of all patentapplications is incorporated herein by reference in its entirety.

FIELD

This disclosure relates generally to battery cells, and moreparticularly, to binders for wet and dry lamination of battery cells.

BACKGROUND

Battery cells are often manufactured using lamination processes thatadhere a separator to one or more electrodes, such as a cathode or ananode. These lamination processes may involve “wet” processes, where theseparator is soaked in electrolyte fluid, or “dry” processes, whereelectrolyte fluid is absent in the separator. During manufacturing, abattery cell may experience a combination “wet” lamination processes and“dry” lamination processes. To facilitate adhesion of the separator tothe electrodes, the separator includes a binder, which may be depositedas a coating thereon. Binders suitable for both “wet” laminationprocesses and “dry lamination “processes” are desirable in batterymanufacturing.

SUMMARY

The embodiments presented herein relate to cell stacks that includebinders for wet and dry lamination processes. The cell stacks, whenlaminated, produce battery cells (or portions thereof). The cell stacksinclude a cathode having a cathode active material disposed on a cathodecurrent collector. The cell stacks also include an anode having an anodeactive material disposed on an anode current collector. The anode isoriented towards the cathode such that the anode active material facesthe cathode active material. A separator is disposed between the cathodeactive material and the anode active material and comprising a bindercomprising a PVdF-HFP copolymer. In certain instances, an electrolytefluid is in contact with the separator.

In some variations, the PVdF-HFP copolymer has a molecular weightgreater than or equal to 1,000,000 u and a weight percent of HFP from 5to 15 percent. In other variations, the binder is a blended binder thatincludes a first PVdF-HFP copolymer and a second PVdF-HFP copolymer. Thefirst PVdF-HFP copolymer has a first molecular weight greater than orequal to 1,000,000 u and a first weight percent of HFP less than orequal to 7 percent. The second PVdF-HFP copolymer has a second molecularweight from 500,000 to 1,000,000 u and a second weight percent of HFPfrom 10 to 15 percent.

The embodiments presented herein also describe methods for laminatingcell stacks of battery cells. The methods may involve both wet and drylamination. The methods include the step of contacting a separator witha first active material of a first electrode to form a first cell stack.The separator includes a binder comprising a PVdF-HFP copolymer. Themethods also include the step of heating the first cell stack tolaminate the separator to the first electrode. In certain instances, themethods additionally include soaking the separator with an electrolytefluid before heating the first cell stack.

In some variations of the methods, the PVdF-HFP copolymer has amolecular weight greater than or equal to 1,000,000 u and a weightpercent of HFP from 5 to 15 percent. In other variations of the methods,the binder is a blended binder that includes a first PVdF-HFP copolymerand a second PVdF-HFP copolymer. The first PVdF-HFP copolymer has afirst molecular weight greater than or equal to 1,000,000 u and a firstweight percent of HFP less than or equal to 7 percent. The secondPVdF-HFP copolymer has a second molecular weight from 500,000 to1,000,000 u and a second weight percent of HFP from 10 to 15 percent.

Other cell stacks and methods of laminating are presented.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 is a top-down view of a battery cell in accordance with anillustrative embodiment;

FIG. 2 is a side view of a set of layers for a battery cell inaccordance with an illustrative embodiment;

FIG. 3A is a side view of a cell stack having a binder suitable for bothwet lamination and dry lamination, according to an illustrativeembodiment;

FIG. 3B is a side view of the cell stack of FIG. 3A, but in which theseparator includes ceramic layers, according to an illustrativeembodiment; and

FIG. 4 is a plot of data representing a peel strength of a cell stackformed using a blended binder, according to an illustrative embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

FIG. 1 presents a top-down view of a battery cell 100 in accordance withan embodiment. The battery cell 100 may correspond to a lithium-ion orlithium-polymer battery cell that is used to power a device used in aconsumer, medical, aerospace, defense, and/or transportationapplication. The battery cell 100 includes a stack 102 containing anumber of layers that include a cathode with a cathode active coating, aseparator, and an anode with an anode active coating. More specifically,the stack 102 may include one strip of cathode active material (e.g.,aluminum foil coated with a lithium compound) and one strip of anodeactive material (e.g., copper foil coated with carbon). The stack 102also includes one strip of separator material (e.g., a microporouspolymer membrane or non-woven fabric mat) disposed between the one stripof cathode active material and the one strip of anode active material.The cathode, anode, and separator layers may be left flat in a planarconfiguration or may be wrapped into a wound configuration (e.g., a“jelly roll”).

During assembly of the battery cell 100, the stack 102 can be enclosedin a flexible pouch. The stack 102 may be in a planar or woundconfiguration, although other configurations are possible. The flexiblepouch is formed by folding a flexible sheet along a fold line 112. Insome instances, the flexible sheet is made of aluminum with a polymerfilm, such as polypropylene. After the flexible sheet is folded, theflexible sheet can be sealed, for example, by applying heat along a sideseal 110 and along a terrace seal 108. The flexible pouch may be lessthan or equal to 120 microns thick to improve the packaging efficiencyof the battery cell 100, the density of battery cell 100, or both.

The stack 102 also includes a set of conductive tabs 106 coupled to thecathode and the anode. The conductive tabs 106 may extend through sealsin the pouch (for example, formed using sealing tape 104) to provideterminals for the battery cell 100. The conductive tabs 106 may then beused to electrically couple the battery cell 100 with one or more otherbattery cells to form a battery pack. For example, the battery pack maybe formed by coupling the battery cells in a series, parallel, or aseries-and-parallel configuration. Such coupled cells may be enclosed ina hard case to complete the battery pack, or may be embedded within anenclosure of a portable electronic device, such as a laptop computer,tablet computer, mobile phone, personal digital assistant (PDA), digitalcamera, and/or portable media player.

FIG. 2 presents a side view of a set of layers for a battery cell (e.g.,the battery cell 100 of FIG. 1) in accordance with the disclosedembodiments. The set of layers may include a cathode current collector202, a cathode active coating 204, a separator 206, an anode activecoating 208, and an anode current collector 210. The cathode currentcollector 202 and the cathode active coating 204 may form a cathode forthe battery cell, and the anode current collector 210 and the anodeactive coating 208 may form an anode for the battery cell. To create thebattery cell, the set of layers may be stacked in a planarconfiguration, or stacked and then wrapped into a wound configuration.Before assembly of the battery cell, the set of layers may correspond toa cell stack.

As mentioned above, the cathode current collector 202 may be an aluminumfoil, the cathode active coating 204 may be a lithium compound, theanode current collector 210 may be a copper foil, the anode activecoating 208 may be carbon, and the separator 206 may include amicroporous polymer membrane or non-woven fabric mat. Non-limitingexamples of the microporous polymer membrane or non-woven fabric matinclude microporous polymer membranes or non-woven fabric mats ofpolyethylene (PE), polypropylene (PP), polyamide (PA),polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyester, andpolyvinylidene difluoride (PVdF). However, other microporous polymermembranes or non-woven fabric mats are possible (e.g., gel polymerelectrolytes).

In general, separators represent structures in a battery, such asinterposed layers, that prevent physical contact of cathodes and anodeswhile allowing ions to transport therebetween. Separators are formed ofmaterials having pores that provide channels for ion transport, whichmay include absorbing an electrolyte fluid that contains the ions.Materials for separators may be selected according to chemicalstability, porosity, pore size, permeability, wettability, mechanicalstrength, dimensional stability, softening temperature, and thermalshrinkage. These parameters can influence battery performance and safetyduring operation.

Separators may incorporate binders to improve adhesion to adjacentelectrode layers (i.e., layers of the cathode and the anode). Thesebinders may also allow ceramic materials to adhere to separators (e.g.,fillers and layers), thereby increasing a separator's mechanicalstrength and resistance to thermal shrinkage. Materials for binders maybe selected according to a wet lamination process, where the set oflayers of the battery cell is laminated with a separator soaked inelectrolyte fluid, and a dry lamination process, where the set of layersof the battery cell is laminated using a separator without electrolytefluid. Binders that allow the battery cell to undergo both wetlamination and dry lamination can be advantageous in reducing materialand processing complexities for battery cell manufacturing.

FIG. 3A presents a side view of a cell stack 300 having a binder 302suitable for both wet lamination and dry lamination, according to anillustrative embodiment. The cell stack 300, when laminated, may producea lithium-ion battery cell. The cell stack 300 includes a cathode 304having a cathode active material 306 disposed on a cathode currentcollector 308. The cell stack 300 also includes an anode 310 having ananode active material 312 disposed on an anode current collector 314.The anode 310 is oriented with respect to the cathode 304 such that theanode active material 312 faces the cathode active material 306.

A separator 316 is disposed between the cathode active material 306 andthe anode active material 312 and includes a binder 302 comprising apolyvinylidene difluoride-hexafluoropropylene copolymer (i.e., aPVdF-HFP copolymer). In some embodiments, the cell stack 300 furtherincludes an electrolyte fluid in contact with the separator 316. Inthese embodiments, the separator 316 may be soaked in the electrolytefluid. The electrolyte fluid may be any type of electrolyte fluidsuitable for battery cells. Non-limiting examples of the electrolytefluid include propylene carbonate, ethylene carbonate, dimethylcarbonate, diethyl carbonate, and ethyl-methyl carbonate. Theelectrolyte fluid may also have a salt dissolved therein. The salt maybe any type of salt suitable for battery cells. For example, and withoutlimitation, salts for a lithium-ion battery cell include LiPF₆, LiBF₄,LiClO₄, LiSO₃CF₃, LiN(SO₂CF₃)₂, LiBC₄O₈, Li[PF₃(C₂CF₅)₃], andLiC(SO₂CF₃)₃. Other salts are possible, including combinations of salts.

Separator 316 may include a microporous polymer membrane or non-wovenfabric mat 318, as shown in FIG. 3A. The microporous polymer membrane ornon-woven fabric mat 318 may be any type of microporous polymer membraneor non-woven fabric mat suitable for battery cells (e.g., a polymermembrane, a gel polymer, etc.). Non-limiting examples of the microporouspolymer membrane or non-woven fabric mat 318 include microporous polymermembranes or non-woven fabric mats of polyethylene (PE), polypropylene(PP), polyamide (PA), polytetrafluoroethylene (PTFE), polyvinyl chloride(PVC), polyester, and polyvinylidene difluoride (PVdF). In someinstances, the separator 316 incorporates ceramic particles therein(i.e., as a filler), which may involve the binder 302, the woven ornon-woven type microporous membrane 318, or both. Non-limiting examplesof ceramic materials for the ceramic particles include magnesium oxidematerials (e.g., Mg(OH)₂, MgO, etc.) and aluminum oxide materials (e.g.,Al₂O₃). Other ceramic materials, however, are possible.

In FIG. 3A, the binder 302 is depicted as layers disposed on themicroporous polymer membrane or non-woven fabric mat 318. However, thisdepiction is not intended as limiting. For example, and withoutlimitation, the binder 302 may also be present, in whole or in part,within pores of the microporous polymer membrane or non-woven fabric mat318. Other configurations of the binder 302 are possible.

The PVdF-HFP copolymer of the binder 302 may have a molecular weight, aweight percent HFP, an acid value, or any combination thereof, thatallows the battery stack 300 to be manufactured using a wet laminationprocess, a dry lamination process, or both. Without wishing to belimited to a particular theory or mode of action, PVdF is asemi-crystalline polymer material with a relatively high meltingtemperature (i.e., T_(m)>170° C.) and a low swelling in electrolytefluid. Progressive incorporation of HFP into the semi-crystallinepolymer material (i.e., of PVdF) yields a copolymer of increasingamorphous content, decreasing melting temperature, and increasingswelling in electrolyte fluid. By selecting the molecular weight and theweight percent of HFP, these properties can be manipulated to bettersuit the copolymer to wet lamination processing, dry laminationprocessing, or both. However, it will be appreciated that suitabilityfor dry lamination may run counter to suitability for wet lamination(and vice versa).

For example, and without limitation, the weight percent of HFP can beincreased to lower a softening point of the copolymer, making thecopolymer more suitable for dry lamination. However, this increase inweight percent also increases a susceptibility of the copolymer toswelling during wet lamination. Swelling during wet lamination candegrade contact between the separator 316 and adjacent cathode 304 andanode 310, which can result in a loss of contact area.

In another non-limiting example, a molecular weight of the PVdF-HFPcopolymer may be increased to improve an interaction of the copolymerwith components contacted by the binder 302 (e.g., the microporouspolymer membrane or non-woven fabric mat 318, the cathode activematerial 306, the anode active material 312, etc.). Such improvedinteraction can enhance adhesion during wet or dry lamination. However,increasing the molecular weight may also increase the softening point ofthe copolymer, making the copolymer less suitable for dry lamination.

In yet another non-limiting example, an amorphous content of thePVdF-HFP copolymer may be increased to improve a coating of thecopolymer onto components contacted by the binder 302 (e.g., themicroporous polymer membrane or non-woven fabric mat 318, the cathodeactive material 306, the anode active material 312, etc.). Higheramorphous content in the copolymer can increase its ductility and lowera risk of microvoids between the copolymer and contacted components.However, increasing the amorphous content may also increase the degreeof swelling of the copolymer, making the copolymer less suitable for wetlamination.

The embodiments disclosed herein are directed towards binders thatcomprise a PVdF-HFP copolymer with a molecular weight and a weightpercent HFP suitable for both wet and dry processing. Moreover, thePVdF-HFP copolymer has an acid value that corresponds to enhancedadhesion of the binder 302 to components of the cell stack 300 (e.g.,the microporous polymer membrane or non-woven fabric mat 318, thecathode active material 306, the anode active material 312, etc.) Theacid value characterizes a quantity of acidic functional groups disposedalong a polymer chain of the PVdF-HFP copolymer. The presence of thesefunctional groups can improve bonding of the PVdF-HFP copolymer tocomponents contacted by the binder 302. Non-limiting examples of acidicfunctional groups include carboxyl groups (e.g., formic acid, aceticacid, etc.) and hydroxyl groups. Other acid functional groups, however,are possible.

In various aspects, the acid value is a quantity of base required toneutralize an acidity of a given quantity of chemical substance. As usedherein, the acid value refers to a number of milligrams of potassiumhydroxide needed to neutralize a given number of grams of PVdF-HFPcopolymer. Other equivalent units of measurement, however, are possiblefor the acid value. Techniques to determine the acid value (and theircorresponding measurement units) are known to those skilled in the artand will not be discussed further.

In one variation, the PVdF-HFP copolymer has a molecular weight greaterthan or equal to 1,000,000 u and a weight percent of HFP from 5 to 15percent. In further embodiments, the PVdF-HFP copolymer has an acidvalue from 3 to 15 milligrams of potassium hydroxide per gram ofcopolymer. In further embodiments, the PVdF-HFP copolymer has an acidvalue from 1.5 to 15 milligrams of potassium hydroxide per gram ofcopolymer.

In some embodiments, the PVdF-HFP copolymer has a molecular weightgreater than or equal to 1,000,000 u and a weight percent of HFP greaterthan or equal to 5 percent. In some embodiments, the PVdF-HFP copolymerhas a molecular weight greater than or equal to 1,000,000 u and a weightpercent of HFP greater than or equal to 10 percent. In some embodiments,the PVdF-HFP copolymer has a molecular weight greater than or equal to1,000,000 u and a weight percent of HFP greater than or equal to 15percent. In some embodiments, the PVdF-HFP copolymer has a molecularweight greater than or equal to 1,000,000 u and a weight percent of HFPgreater than or equal to 20 percent.

In some embodiments, the PVdF-HFP copolymer has a molecular weightgreater than or equal to 1,000,000 u and a weight percent of HFP lessthan or equal to 25 percent. In some embodiments, the PVdF-HFP copolymerhas a molecular weight greater than or equal to 1,000,000 u and a weightpercent of HFP less than or equal to 20 percent. In some embodiments,the PVdF-HFP copolymer has a molecular weight greater than or equal to1,000,000 u and a weight percent of HFP less than or equal to 15percent. In some embodiments, the PVdF-HFP copolymer has a molecularweight greater than or equal to 1,000,000 u and a weight percent of HFPless than or equal to 10 percent.

In some embodiments, the PVdF-HFP copolymer has an acid value greaterthan or equal to 1.5 milligrams of potassium hydroxide per gram ofcopolymer. In some embodiments, the PVdF-HFP copolymer has an acid valuegreater than or equal to 1.8 milligrams of potassium hydroxide per gramof copolymer. In some embodiments, the PVdF-HFP copolymer has an acidvalue greater than or equal to 3 milligrams of potassium hydroxide pergram of copolymer. In some embodiments, the PVdF-HFP copolymer has anacid value greater than or equal to 8 milligrams of potassium hydroxideper gram of copolymer. In some embodiments, the PVdF-HFP copolymer hasan acid value greater than or equal to 13 milligrams of potassiumhydroxide per gram of copolymer. In some embodiments, the PVdF-HFPcopolymer has an acid value greater than or equal to 12 milligrams ofpotassium hydroxide per gram of copolymer. In some embodiments, thePVdF-HFP copolymer has an acid value greater than or equal to 18milligrams of potassium hydroxide per gram of copolymer.

In some embodiments, the PVdF-HFP copolymer has an acid value less than20 milligrams of potassium hydroxide per gram of copolymer. In someembodiments, the PVdF-HFP copolymer has an acid value less than or equalto 15 milligrams of potassium hydroxide per gram of copolymer. In someembodiments, the PVdF-HFP copolymer has an acid value less than or equalto 10 milligrams of potassium hydroxide per gram of copolymer. In someembodiments, the PVdF-HFP copolymer has an acid value less than or equalto 5 milligrams of potassium hydroxide per gram of copolymer.

In another variation, the binder 302 of the separator 316 is a blendedbinder including a first PVdF-HFP copolymer and a second PVdF-HFPcopolymer. The first PVdF-HFP copolymer has a first molecular weightgreater than or equal to 1,000,000 u and a first weight percent of HFPless than or equal to 7 percent. The second PVdF-HFP copolymer has asecond molecular weight from 500,000 to 1,000,000 u and a second weightpercent of HFP from 10 to 15 percent. In further embodiments, the firstPVdF-HFP copolymer and the second PVdF-HFP copolymer have respectiveacid values from 1.5 to 15 milligrams of potassium hydroxide per gram ofcopolymer.

In some variations, the first PVdF-HFP copolymer and the second PVdF-HFPcopolymer have acid values from 1.5 to 15 milligrams of potassiumhydroxide per gram of copolymer. In some variations, the first PVdF-HFPcopolymer has a first acid value from 1.8 to 2.4 milligrams of potassiumhydroxide per gram of copolymer. In some variations, the first PVdF-HFPcopolymer has a first acid value of 2.1 milligrams of potassiumhydroxide per gram of copolymer. In some variations, the second PVdF-HFPcopolymer has a second acid value from 12.3 to 12.9 milligrams ofpotassium hydroxide per gram of copolymer. In some variations, thesecond PVdF-HFP copolymer has a second acid value of 12.6 milligrams ofpotassium hydroxide per gram of copolymer. It will be recognized thatthe first acid value and second acid value described herein can becombined in any variation.

In some embodiments, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP less than or equal to 10 percent. In some embodiments, the firstPVdF-HFP copolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP less than or equal to 8percent. In some embodiments, the first PVdF-HFP copolymer has a firstmolecular weight greater than or equal to 1,000,000 u and a first weightpercent of HFP less than or equal to 6 percent. In some embodiments, thefirst PVdF-HFP copolymer has a first molecular weight greater than orequal to 1,000,000 u and a first weight percent of HFP less than orequal to 4 percent. In some embodiments, the first PVdF-HFP copolymerhas a first molecular weight greater than or equal to 1,000,000 u and afirst weight percent of HFP less than or equal to 2 percent.

In some embodiments, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 1 to 3 percent. In some embodiments, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 3 to 5 percent. Insome embodiments, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 5 to 7 percent. In some embodiments, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 7 to 9 percent.

In some embodiments, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 1 to 9 percent. In some embodiments, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 3 to 7 percent. Insome embodiments, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 1 to 5 percent. In some embodiments, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 5 to 9 percent.

In some embodiments, the second PVdF-HFP copolymer has a secondmolecular weight greater than or equal to 750,000 u and a second weightpercent of HFP less than 14 percent. In some embodiments, the secondPVdF-HFP copolymer has a second molecular weight greater than or equalto 750,000 u and a second weight percent of HFP less than 13 percent. Insome embodiments, the second PVdF-HFP copolymer has a second molecularweight greater than or equal to 750,000 u and a second weight percent ofHFP less than 12 percent. In some embodiments, the second PVdF-HFPcopolymer has a second molecular weight greater than or equal to 750,000u and a second weight percent of HFP less than 11 percent.

In some embodiments, the second PVdF-HFP copolymer has a secondmolecular weight greater than or equal to 750,000 u and a second weightpercent of HFP greater than 11 percent. In some embodiments, the secondPVdF-HFP copolymer has a second molecular weight greater than or equalto 750,000 u and a second weight percent of HFP greater than 12 percent.In some embodiments, the second PVdF-HFP copolymer has a secondmolecular weight greater than or equal to 750,000 u and a second weightpercent of HFP greater than 13 percent. In some embodiments, the secondPVdF-HFP copolymer has a second molecular weight greater than or equalto 750,000 u and a second weight percent of HFP greater than 14 percent.

In some embodiments, the second PVdF-HFP copolymer has a secondmolecular weight less than or equal to 750,000 u and a second weightpercent of HFP less than 14 percent. In some embodiments, the secondPVdF-HFP copolymer has a second molecular weight less than or equal to750,000 u and a second weight percent of HFP less than 13 percent. Insome embodiments, the second PVdF-HFP copolymer has a second molecularweight less than or equal to 750,000 u and a second weight percent ofHFP less than 12 percent. In some embodiments, the second PVdF-HFPcopolymer has a second molecular weight less than or equal to 750,000 uand a second weight percent of HFP less than 11 percent.

In some embodiments, the second PVdF-HFP copolymer has a secondmolecular weight less than or equal to 750,000 u and a second weightpercent of HFP greater than 11 percent. In some embodiments, the secondPVdF-HFP copolymer has a second molecular weight less than or equal to750,000 u and a second weight percent of HFP greater than 12 percent. Insome embodiments, the second PVdF-HFP copolymer has a second molecularweight less than or equal to 750,000 u and a second weight percent ofHFP greater than 13 percent. In some embodiments, the second PVdF-HFPcopolymer has a second molecular weight less than or equal to 750,000 uand a second weight percent of HFP greater than 14 percent.

In certain variations of the cell stack 300, the separator 316 includesa polyolefin layer having a first side 320 and a second side 322 (i.e.,the microporous polymer membrane or non-woven fabric mat 318 is apolyolefin layer). Non-limiting examples of the polyolefin layer includea polyethylene layer, a polypropylene layer, a layer having of a blendof polyethylene and polypropylene, and combinations thereof. The firstside 320 forms a first interface 324 with the cathode active material306. The second side 322 forms a second interface 326 with the anodeactive material 312. The binder 302 (or portions thereof) may bedisposed as layers along the first interface 324 and the secondinterface 326 as shown in FIG. 3A.

In these variations of the cell stack 300, ceramic layers may bedisposed along the first interface 324 and the second interface 326.Such ceramic layers may improve a chemical and dimensional stability ofthe separator 316 during operation of the battery stack 300 (i.e., aftermanufacturing). Such ceramic layers may also improve a mechanicalstrength of the separator 316. Non-limiting examples of ceramicmaterials for the ceramic layers include magnesium oxide materials(e.g., Mg(OH)₂, MgO, etc.) and aluminum oxide materials (e.g., Al₂O₃).FIG. 3B presents a side view of the cell stack 300 of FIG. 3A, but inwhich the separator 316 includes ceramic layers, according to anillustrative embodiment.

In some instances, a first ceramic layer 328 is disposed along the firstinterface 324. The first ceramic layer 328 includes a first plurality ofceramic particles in contact with the binder 302. In some instances, asecond ceramic layer 330 is disposed along the second interface 326. Thesecond ceramic layer 330 includes a second plurality of ceramicparticles in contact with the binder 302. In other instances, the firstceramic layer 328 is disposed along the first interface 324 and thesecond ceramic layer 330 is disposed along the second interface 326. Inthese instances, the first ceramic layer 328 includes the firstplurality of ceramic particles in contact with the binder 302 and thesecond ceramic layer 330 includes the second plurality of ceramicparticles in contact with the binder 302.

Contact with the binder 302 may involve ceramic particles blended withthe binder 302. In these instances, the first plurality of ceramicparticles and the second plurality of ceramic particles may represent60-90 wt. % of, respectively, the first ceramic layer 328 and the secondceramic layer 330. In other instances, the first plurality of ceramicparticles and the second plurality of ceramic particles represent lessthan or equal to 50 wt. % of, respectively, the first ceramic layer 328and the second ceramic layer 330. In still other instances, the firstplurality of ceramic particles and the second plurality of ceramicparticles represent greater than or equal to 90 wt. % of, respectively,the first ceramic layer 328 and the second ceramic layer 330.

Contact with the binder 302 may also involve ceramic particlescontacting layers of the binder 302. Such layers of the binder 302 maybe interposed between the first ceramic layer 328 and the cathode activematerial 306, between the second ceramic layer 330 and the anode activematerial 312, or any combination thereof.

FIG. 4 presents a plot of data representing a peel strength of a cellstack formed using a blended binder, according to an illustrativeembodiment. The peel strength of the cell stack is indicated on theordinate. The abscissa indicates peel strengths corresponding to dry andwet lamination processes. For each lamination process, a cell stack wasformed using a separator adhered to a cathode or and a separator adheredto an anode. Thus, the plot of data presents four conditions for whichpeel strengths were measured.

Three different binders were used for each condition, including aconventional (non-blended) binder, a first blended binder, and a secondblended binder. The conventional binder had a PVdF-HFP copolymer with amolecular weight of 1,200,000 u, a weight percent of HFP of 6 percent,and an acid value of 1 milligrams of potassium hydroxide per gram ofcopolymer. The first blended binder had a first PVdF-HFP copolymer witha molecular weight of 1,100,000 u, a weight percent of HFP of 5 percent,and an acid value of 13 milligrams of potassium hydroxide per gram ofcopolymer, and a second PVdF-HFP copolymer with a molecular weight of1,200,000 u, a weight percent of HFP of zero, and an acid value of 10milligrams of potassium hydroxide per gram of copolymer. The secondblended binder had a first PVdF-HFP copolymer with a molecular weight of1,100,000 u, a weight percent of HFP of 5 percent, and an acid value of13 milligrams of potassium hydroxide per gram of copolymer, and a secondPVdF-HFP copolymer with a molecular weight of 860,000 u, a weightpercent of HFP of 12 percent, and an acid value of 2 milligrams ofpotassium hydroxide per gram of copolymer.

Separators in the cell stacks included a first ceramic layer and asecond ceramic layer coated on opposite sides of a polyethylene basefilm. The first and second ceramic layers were prepared from blendscorresponding to 70 wt. % of Mg(OH)₂ and 30 wt. % of the blended binder.The first and second ceramic layers were solution-cast onto separatorsof the cell stacks. Activation temperatures for the wet and drylamination processes were 85° C. The cathode active material in thecathode included a mixture of lithium cobalt oxide material, PVdFbinder, and active carbon. The anode active material in the anodeincluded graphite, SBR, and CMC. To laminate the cell stack, a pressureof about 1 MPa was applied.

In FIG. 4, the peel strengths of the first and second blended bindersare clearly higher than those of the conventional (non-blended) binder.Moreover, in all conditions, the second blended binder exhibits peelstrengths that exceed 1.5 N/m. In contrast, peel strengths of theconventional binder are below 1.5 N/m for all conditions. The firstblended binder meets or exceeds 1.5 N/m in all conditions expect whenadhering the separator to the anode in a wet process. However, it willbe appreciated that the first and second blended binder are bothsuitable for use in wet and dry processing.

It will be appreciated that those skilled in the art may utilizetechniques of differential scanning calorimetry (DSC) to differentiatebetween melting temperatures of blended binders using heat flowprofiles. Such heat flow profiles may allow weight percentages to bedetermined for PVdF-HFP copolymers within the blended binders. Moreover,those skilled in the art may also utilize gel permeation chromatography(GPC) to determine molecular weights of PVdF-HFP copolymers within theblended binders.

According to an illustrative embodiment, a method for laminating atleast one cell stack of a battery cell includes the step of contacting aseparator with a first active material of a first electrode to form afirst cell stack. The separator includes a binder comprising a PVdF-HFPcopolymer. The PVdF-HFP copolymer has a molecular weight greater than orequal to 1,000,000 u and a weight percent of HFP from 5 to 15 percent.In some embodiments, the PVdF-HFP copolymer has an acid value from 3 to15 milligrams of potassium hydroxide per gram of copolymer. In someembodiments, the PVdF-HFP copolymer has an acid value from 1.5 to 15milligrams of potassium hydroxide per gram of copolymer.

The method also includes the step of heating the first cell stack tolaminate the separator to the first electrode. The first active materialof the first electrode may be a cathode active material of a cathode oran anode active material of an anode. In some embodiments, the methodadditionally includes the step of, before heating the first cell stack,soaking the separator with an electrolyte fluid. In some embodiments,the method additionally includes the step of, after heating the firstcell stack, soaking the separator with the electrolyte fluid and heatingthe first cell stack again. It will be appreciated that a presence orabsence of electrolyte fluid in the separator corresponds to,respectively, a wet lamination process and a dry lamination process.

In some variations, the PVdF-HFP copolymer has a molecular weightgreater than or equal to 1,000,000 u and a weight percent of HFP from 5to 15 percent. In further variations, the PVdF-HFP copolymer has an acidvalue from 3 to 15 milligrams of potassium hydroxide per gram ofcopolymer. In further variations, the PVdF-HFP copolymer has an acidvalue from 1.5 to 15 milligrams of potassium hydroxide per gram ofcopolymer.

In some variations, the PVdF-HFP copolymer has a molecular weightgreater than or equal to 1,000,000 u and a weight percent of HFP greaterthan or equal to 5 percent. In some variations, the PVdF-HFP copolymerhas a molecular weight greater than or equal to 1,000,000 u and a weightpercent of HFP greater than or equal to 10 percent. In some variations,the PVdF-HFP copolymer has a molecular weight greater than or equal to1,000,000 u and a weight percent of HFP greater than or equal to 15percent. In some variations, the PVdF-HFP copolymer has a molecularweight greater than or equal to 1,000,000 u and a weight percent of HFPgreater than or equal to 20 percent.

In some variations, the PVdF-HFP copolymer has a molecular weightgreater than or equal to 1,000,000 u and a weight percent of HFP lessthan or equal to 25 percent. In some variations, the PVdF-HFP copolymerhas a molecular weight greater than or equal to 1,000,000 u and a weightpercent of HFP less than or equal to 20 percent. In some variations, thePVdF-HFP copolymer has a molecular weight greater than or equal to1,000,000 u and a weight percent of HFP less than or equal to 15percent. In some variations, the PVdF-HFP copolymer has a molecularweight greater than or equal to 1,000,000 u and a weight percent of HFPless than or equal to 10 percent.

In some variations, the PVdF-HFP copolymer has an acid value greaterthan or equal to 1.5 milligrams of potassium hydroxide per gram ofcopolymer. In some variations, the PVdF-HFP copolymer has an acid valuegreater than or equal to 3 milligrams of potassium hydroxide per gram ofcopolymer. In some variations, the PVdF-HFP copolymer has an acid valuegreater than or equal to 8 milligrams of potassium hydroxide per gram ofcopolymer. In some variations, the PVdF-HFP copolymer has an acid valuegreater than or equal to 13 milligrams of potassium hydroxide per gramof copolymer. In some variations, the PVdF-HFP copolymer has an acidvalue greater than or equal to 12 milligrams of potassium hydroxide pergram of copolymer. In some variations, the PVdF-HFP copolymer has anacid value greater than or equal to 18 milligrams of potassium hydroxideper gram of copolymer.

In some variations, the PVdF-HFP copolymer has an acid value less than20 milligrams of potassium hydroxide per gram of copolymer. In somevariations, the PVdF-HFP copolymer has an acid value less than or equalto 15 milligrams of potassium hydroxide per gram of copolymer. In somevariations, the PVdF-HFP copolymer has an acid value less than or equalto 10 milligrams of potassium hydroxide per gram of copolymer. In somevariations, the PVdF-HFP copolymer has an acid value less than or equalto 5 milligrams of potassium hydroxide per gram of copolymer.

In some embodiments, the step of contacting the separator with the firstactive material of the first electrode includes contacting the separatorwith a second active material of a second electrode. In theseembodiments, the separator is disposed between the first electrode andthe second electrode to form the first cell stack. The step of heatingthe first cell stack laminates the separator to both the first electrodeand the second electrode. In certain instances, the method includes thestep of, before heating the first cell stack, soaking the separator withthe electrolyte fluid. In other instances, the method includes the stepof, after heating the first cell stack, soaking the separator with theelectrolyte fluid and re-heating the first cell stack.

In other embodiments, the method further includes the step of contactingthe separator of the first cell stack with the second active material ofthe second electrode, thereby forming a second cell stack. The methodalso includes the step of heating the second cell stack to laminate theseparator to the second electrode. In certain instances, the method mayinvolve the step of, before heating the second cell stack, soaking theseparator with an electrolyte fluid. In other instances, the method mayinvolve the step of, after heating the second cell stack, soaking theseparator with the electrolyte fluid and then heating the second cellstack again.

In still other embodiments, the method includes the step of, beforeheating the first cell stack, soaking the separator with the electrolytefluid. In such embodiments, the method also includes the step of, afterheating the first cell stack, contacting the separator of the first cellstack with the second active material of the second electrode, therebyforming the second cell stack. The second cell stack is heated tolaminate the separator to the second electrode. In certain instances,the method may involve the step of, before heating the second cellstack, soaking the separator with an electrolyte fluid. In otherinstances, the method may involve the step of, after heating the secondcell stack, soaking the separator with the electrolyte fluid and thenheating the second cell stack again.

According to another illustrative embodiment, a method for laminating atleast one cell stack of battery cell includes the step of contacting aseparator with a first active material of a first electrode to form afirst cell stack. The separator includes a blended binder comprising afirst PVdF-HFP copolymer and a second PVdF-HFP copolymer. The firstPVdF-HFP copolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP less than or equal to 7percent. The second PVdF-HFP copolymer has a second molecular weightfrom 500,000 to 1,000,000 u and a second weight percent of HFP from 10to 15 percent. In some embodiments, first PVdF-HFP copolymer and thesecond PVdF-HFP copolymer have respective acid values from 3 to 15milligrams of potassium hydroxide per gram of copolymer.

The method also includes the step of heating the first cell stack tolaminate the separator to the first electrode. The first active materialof the first electrode may be a cathode active material of a cathode oran anode active material of an anode. In some embodiments, the methodadditionally includes the step of, before heating the first cell stack,soaking the separator with an electrolyte fluid. In some embodiments,the method additionally includes the step of, after heating the firstcell stack, soaking the separator with the electrolyte fluid and heatingthe first cell stack again. It will be appreciated that a presence orabsence of electrolyte fluid in the separator corresponds to,respectively, a wet lamination process and a dry lamination process.

In some variations, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP less than or equal to 10 percent. In some variations, the firstPVdF-HFP copolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP less than or equal to 8percent. In some variations, the first PVdF-HFP copolymer has a firstmolecular weight greater than or equal to 1,000,000 u and a first weightpercent of HFP less than or equal to 6 percent. In some variations, thefirst PVdF-HFP copolymer has a first molecular weight greater than orequal to 1,000,000 u and a first weight percent of HFP less than orequal to 4 percent. In some variations, the first PVdF-HFP copolymer hasa first molecular weight greater than or equal to 1,000,000 u and afirst weight percent of HFP less than or equal to 2 percent.

In some variations, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 1 to 3 percent. In some variations, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 3 to 5 percent. Insome variations, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 5 to 7 percent. In some variations, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 7 to 9 percent.

In some variations, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 1 to 9 percent. In some variations, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 3 to 7 percent. Insome variations, the first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 u and a first weight percentof HFP from 1 to 5 percent. In some variations, the first PVdF-HFPcopolymer has a first molecular weight greater than or equal to1,000,000 u and a first weight percent of HFP from 5 to 9 percent.

In some variations, the second PVdF-HFP copolymer has a second molecularweight greater than or equal to 750,000 u and a second weight percent ofHFP less than 14 percent. In some variations, the second PVdF-HFPcopolymer has a second molecular weight greater than or equal to 750,000u and a second weight percent of HFP less than 13 percent. In somevariations, the second PVdF-HFP copolymer has a second molecular weightgreater than or equal to 750,000 u and a second weight percent of HFPless than 12 percent. In some variations, the second PVdF-HFP copolymerhas a second molecular weight greater than or equal to 750,000 u and asecond weight percent of HFP less than 11 percent.

In some variations, the second PVdF-HFP copolymer has a second molecularweight greater than or equal to 750,000 u and a second weight percent ofHFP greater than 11 percent. In some variations, the second PVdF-HFPcopolymer has a second molecular weight greater than or equal to 750,000u and a second weight percent of HFP greater than 12 percent. In somevariations, the second PVdF-HFP copolymer has a second molecular weightgreater than or equal to 750,000 u and a second weight percent of HFPgreater than 13 percent. In some variations, the second PVdF-HFPcopolymer has a second molecular weight greater than or equal to 750,000u and a second weight percent of HFP greater than 14 percent.

In some variations, the second PVdF-HFP copolymer has a second molecularweight less than or equal to 750,000 u and a second weight percent ofHFP less than 14 percent. In some variations, the second PVdF-HFPcopolymer has a second molecular weight less than or equal to 750,000 uand a second weight percent of HFP less than 13 percent. In somevariations, the second PVdF-HFP copolymer has a second molecular weightless than or equal to 750,000 u and a second weight percent of HFP lessthan 12 percent. In some variations, the second PVdF-HFP copolymer has asecond molecular weight less than or equal to 750,000 u and a secondweight percent of HFP less than 11 percent.

In some variations, the second PVdF-HFP copolymer has a second molecularweight less than or equal to 750,000 u and a second weight percent ofHFP greater than 11 percent. In some variations, the second PVdF-HFPcopolymer has a second molecular weight less than or equal to 750,000 uand a second weight percent of HFP greater than 12 percent. In somevariations, the second PVdF-HFP copolymer has a second molecular weightless than or equal to 750,000 u and a second weight percent of HFPgreater than 13 percent. In some variations, the second PVdF-HFPcopolymer has a second molecular weight less than or equal to 750,000 uand a second weight percent of HFP greater than 14 percent.

In some embodiments, the step of contacting the separator with the firstactive material of the first electrode includes contacting the separatorwith a second active material of a second electrode. In theseembodiments, the separator is disposed between the first electrode andthe second electrode to form the first cell stack. The step of heatingthe first cell stack laminates the separator to both the first electrodeand the second electrode. In certain instances, the method includes thestep of, before heating the first cell stack, soaking the separator withthe electrolyte fluid. In other instances, the method includes the stepof, after heating the first cell stack, soaking the separator with theelectrolyte fluid and heating the first cell stack again.

In other embodiments, the method further includes the step of contactingthe separator of the first cell stack with the second active material ofthe second electrode, thereby forming a second cell stack. The methodalso includes the step of heating the second cell stack to laminate theseparator to the second electrode. In certain instances, the method mayinvolve the step of, before heating the second cell stack, soaking theseparator with an electrolyte fluid. In other instances, the method mayinvolve the step of, after heating the second cell stack, soaking theseparator with the electrolyte fluid and then heating the second cellstack again.

In still other embodiments, the method includes the step of, beforeheating the first cell stack, soaking the separator with the electrolytefluid. In such embodiments, the method also includes the step of, afterheating the first cell stack, contacting the separator of the first cellstack with the second active material of the second electrode, therebyforming the second cell stack. The second cell stack is heated tolaminate the separator to the second electrode. In certain instances,the method may involve the step of, before heating the second cellstack, soaking the separator with an electrolyte fluid. In otherinstances, the method may involve the step of, after heating the secondcell stack, soaking the separator with the electrolyte fluid and thenheating the second cell stack again.

The cell stacks described herein can be valuable in the manufacturing ofelectronic devices, including battery cells that are fabricated with wetlamination processes, dry lamination processes, or both. An electronicdevice herein can refer to any electronic device known in the art. Forexample, the electronic device can be a telephone, such as a cell phone,and a land-line phone, or any communication device, such as a smartphone, including, for example an iPhone®, an electronic emailsending/receiving device. The electronic device can also be anentertainment device, including a portable DVD player, conventional DVDplayer, Blue-Ray disk player, video game console, music player, such asa portable music player (e.g., iPod®), etc. The electronic device can bea part of a display, such as a digital display, a TV monitor, anelectronic-book reader, a portable web-browser (e.g., iPad®), watch(e.g., AppleWatch), or a computer monitor. The electronic device canalso be a part of a device that provides control, such as controllingthe streaming of images, videos, sounds (e.g., Apple TV®), or it can bea remote control for an electronic device. Moreover, the electronicdevice can be a part of a computer or its accessories, such as the harddrive tower housing or casing, laptop housing, laptop keyboard, laptoptrack pad, desktop keyboard, mouse, and speaker. The anode cells,lithium-metal batteries, and battery packs can also be applied to adevice such as a watch or a clock.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not targeted to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. A battery cell comprising a cell stack, the cellstack comprising: a cathode comprising a cathode active materialdisposed on a cathode current collector; an anode comprising an anodeactive material disposed on an anode current collector, the anodeoriented towards the cathode such that the anode active material facesthe cathode active material; a separator disposed between the cathodeactive material and the anode active material and comprising a blendedbinder comprising a first PVdF-HFP copolymer and a second PVdF-HFPcopolymer; and wherein first PVdF-HFP copolymer has a first molecularweight greater than or equal to 1,000,000 grams per mole and a firstweight percent of HFP less than or equal to 7 percent, and whereinsecond PVdF-HFP copolymer has a second molecular weight from 500,000 to1,000,000 grams per mole and a second weight percent of HFP from 10 to15 percent.
 2. The battery cell of claim 1, wherein in the firstPVdF-HFP copolymer and the second PVdF-HFP copolymer have respectiveacid values from 1.5 to 15 milligrams of potassium hydroxide per gram ofcopolymer.
 3. The battery cell of claim 2, wherein the first PVdF-HFPcopolymer has a first acid value of 2.1 milligrams of potassiumhydroxide per gram of copolymer, and the second PVdF-HFP copolymer has asecond acid value of 12.6 milligrams of potassium hydroxide per gram ofcopolymer.
 4. The battery cell of claim 1, further comprising anelectrolyte fluid in contact with the separator.
 5. The battery cell ofclaim 1, wherein the separator further comprises a polyolefin layercomprising a first side and a second side, the first side forming afirst interface with the cathode active material, the second sideforming a second interface with the anode active material.
 6. Thebattery cell of claim 5, wherein a first ceramic layer is disposed alongthe first interface, the first ceramic layer comprising a firstplurality of ceramic particles in contact with the blended binder. 7.The battery cell of claim 5, wherein a second ceramic layer is disposedalong the second interface, the second ceramic layer comprising a secondplurality of ceramic particles in contact with the blended binder. 8.The battery cell of claim 5, wherein a first ceramic layer is disposedalong the first interface, the first ceramic layer comprising a firstplurality of ceramic particles in contact with the blended binder; andwherein a second ceramic layer is disposed along the second interface,the second ceramic layer comprising a second plurality of ceramicparticles in contact with the blended binder.
 9. A portable electronicdevice comprising a set of components powered by the battery cell ofclaim 1.